DIY Foot Drum

[FrankenWashie]

Back to the original topic, I did some suck-it-and-see-engineering just now. Stuck a disk piezo transducer to the bottom of a small wooder crate and plugged it into my THR set to the bass amp sim. The output was low (no pre-amp) but the audio quality was apparent. Rather than the satisfying thump I am aiming for, I got something more akin to a tap, or a knock, with just a little bit of click mixed in. I don't even think EQ would help (I maxed the amp bass and adjusted mid and treble) since the low frequencies didn't appear to be there to start with. Maybe a different wooden box would help, or wearing boots instead of socks.

To compare, I then hooked the broken 6" sub driver up as a microphone and gave the cone a light tap. From the amp came the rich resonant thumpa thumpa I was looking for with this project. I tested again with the Sanyo speaker I got for the mini amp project, and again, a nice thump from the amp. It was not as rich as the sub driver, but it was still in the ballpark. The piezo wasn't in the ballpark. It wasn't in the car park. I don't even think it was in the right part of town.

I now understand why many of the DIY foot drum designs I looked at use a speaker as the transducer. In this application, more or less faithful reproduction of the vibrations isn't really the goal.

Does that affect the dimensions for the box Dan?

[jugglindan]

Does that affect the dimensions for the box Dan?

Good question. At first I thought it wouldn't, since the 150mm width would be enough for a 4" speaker, or maybe a 5" depending on the timber thickness and internal dimensions. But I am now wondering how much height will be needed. I know speaker drivers vary a lot in depth. Today I will look up dimensions of some of the speakers I might use and get back to you.

DC

[jugglindan]

OK, I have a 5" speaker that has a diameter of 135mm once I include the metal surround. That will easily fit into the 150mm width even if the wood was no more than 6 or 7mm thick. But the speaker is 50mm high (measured with digital calipers). So it's too big, especially the taper from 50mm to 40mm plan. I am happy to keep the box as is, and obtain a smaller diameter speaker. Or the box could have 10mm added to the height (tapering 60 to 50mm). That's getting pretty big though, so maybe keep it as is and I will get a smaller speaker if the piezo doesn't sound right.

DC

[FrankenWashie]

Hmmm... I am pondering how to go about this.
if we make it more wedge shaped, the you might over come the depth issue some what. But we will still end up wit a chunky enclosure.

Out of interest what size piezo did you test?

[jugglindan]

I agree that the box shouldn't get any larger. The speaker I have is just too large (it's a 5"). I can get a generic 4" speaker from Jaycar for $5. It will easily fit into the current planned dimensions. I was just at Jaycar today getting some parts for my current pedal and amp builds. I should have picked up one of the speakers.

The piezo I tested is a 3cm disk. It probably wasn't a totally fair test though, as the box was a bit dinky, making it hard to stomp with my foot. A lot of people use piezo mics in these, so it should work. The box Brendan built looks too small to house a speaker, so I suspect it has a piezo inside.

[Brendan]

That looks awesome Brendan. Very close to the sort of thing I am working towards. I know it's not wired up, but what are you using inside as the microphone? Have you tested with temporary wiring? How does it sound?

DC

Nothing as yet - hence why I'm following intently. Didn't want to stuff it up with a couple of dinky piezo's and haven't really revisited to see alternatives...

[jugglindan]

Nothing as yet - hence why I'm following intently. Didn't want to stuff it up with a couple of dinky piezo's and haven't really revisited to see alternatives...

Ah, I see. Well, I am happy to be the guinea pig
There are three main designs I have seen: piezo, speaker, and a pickup mounted close to a metallic object under the stomping surface. I will try the first two.

[Brendan]

I've got an old p bass pickup kicking around - may see if I can rig that up inside without a full commit.

[jugglindan]

I've got an old p bass pickup kicking around - may see if I can rig that up inside without a full commit.

Great. I think I linked to a design or two like that back on page 1 or 2. I would be very interested to see how it works out, even though I don't have any spare pickups laying around. I like that it is less likely to need a preamp while I am pretty much committed to building a preamp into my mini amp as an optional input.

[FrankenWashie]

So the Lab got a bit busy this afternoon.

I needed to do some rip cutting on a large chunk of QLD Maple and some mahogany that has been laying about.

This involved passing an 8” wide board through my bandsaw, with a 20mm ripping blade on it. Slightly scary. Push sticks mandatory.



I’m building 2 enclosures, one is more or less to the basic box specified by Jugglindan, the other is a FrankenLab twist version.

I decided to use some of the beech I had for the box sides; on the square box for DC, the ends will be Merbau, on the FL version sides and ends are beech.



The tops will be QMaple, the key decision for being 1/4” or 1/2” top?




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